1. Field of the Invention
The present invention relates generally to an optical antenna, and in particular, to an optical antenna that includes an optical concentrator.
2. Description of the Related Art
A typical optical antenna includes a light concentrator in the form of a hemispherical lens. A distinctive shortcoming of this light concentrator is the limited acceptance angle range in which an optical signal is receivable.
To overcome the problem, Warwick University, U.K. proposed a trumpet-shaped light concentrator. The optical antenna is applicable to infrared wireless optical communication systems, a variety of signal processes, analog or digital systems, and portable phones. As one simple example, the optical antenna can be implemented in a wireless remote controller for home use.
FIG. 1 illustrates a conventional optical antenna 100 including a trumpet-shaped light concentrator 110, and an optical detector 120 for detecting an optical signal incident through the light concentrator 110.
Like a trumpet, the light concentrator 110 becomes narrow in width, starting from a first end 110a at which optical signals are incident to a second end 110b contacting the optical detector 120. The light concentrator 110 totally internally reflects to the optical detector 120 the optical signal incident at the first end 10a within an acceptance angle. The acceptance angle refers to an angle over which the optical detector 120 accepts an optical signal incident on the light concentrator 110. The totally internally reflected optical signal from the light concentrator 110 is applied to the input of the optical detector 120.
The optical detector 120 can be a waveguide photodiode (PD). A refraction index matching layer or a band pass filter can be inserted between the light concentrator 110 and the optical detector 120.
FIG. 2 illustrates an operational characteristic of the optical antenna depicted in FIG. 1. An optical signal incident at a larger angle than an acceptance angle is shown. Referring to FIG. 2, the input optical signal is radiated outside the optical concentrator 110 after total reflection.
In the above optical antenna, while the trumpet-shaped light concentrator offers a wider acceptance angle than the hemispherical lens, any incoming optical signal beyond the acceptance angle is re-reflected outside.